The present invention relates to a method and apparatus for controlling the fuel-feeding rate of an internal combustion engine during starting of and for a period of time after starting of the engine.
In an internal combustion engine of the electronic fuel-injection control type having fuel-injection valves or of the electronic carburetor-control type having an electronically controlled carburetor, not only is a normal warm-up enrichment operation for increasing the fuel-feeding rate depending upon the warm-up condition of the engine executed but an engine-starting enrichment operation for additionally increasing the fuel-feeding rate during starting (cranking) is also executed. After starting of the engine, the above-mentioned additional increment according to the starting-enrichment operation is gradually decreased to zero with the lapse of time. Thereafter, normal warm-up enrichment is executed. These enrichment operations (hereinafter referred to as two-characteristic enrichment) are already known by, for example, SAE paper No. 740,020, pages 237 to 244.
During starting of and for a period of time after starting of the engine, since the temperature of the inner wall in the combustion chamber is low, the engine requires a rich air-fuel mixture in order for good operating characteristics to be obtained. Therefore, during starting of and for a while after starting of the engine, the above starting-enrichment operation is carried out. However, since the inner wall temperature rises faster than the coolant temperature, which is, in general, used for detecting the warm-up condition of the engine, the starting-enrichment operation need not be executed until the engine is fully warmed-up. Therefore, after starting of the engine, the starting increment of the fuel-feeding rate is gradually decreased to zero and thereafter fuel increment according to the normal warm-up enrichment operation is executed, causing the emission control characteristics to improve. In other words, the aforementioned two-characteristic enrichment is, thus, executed.
However, according to conventional two-characteristic enrichment, since the speed decrease of the additional fuel increment according to the engine starting-enrichment operation after starting of the engine is always constant, the starting enrichment does not correctly respond to the inner wall temperature of the combustion chamber. In other words, according to the conventional enrichment, the difference of the inner wall temperature, which difference is caused by the difference of the operating condition of the engine after starting, is completely ignored.